Since vehicles have widely been used as a transportation means, air pollution has become a serious problem. Almost 70% of all motorcycles use a two-stroke engine, which forms a major pollution source. Although all new motorcycles have been inspected and adjusted before leaving the factory to comply with the exhaust emission regulations, most used motorcycles have a higher pollution level than standards allow as a result of maintenance and operation negligence. Moreover, besides polluted air quality, engine malfunction and damage to parts also exist. It seems an adverse cycle in terms of air pollution.